Eq Pedal Weird Response

[Baran Ismen]

Hi everyone.

I have recently gotten a mxr 10 band eq clone from aliex, its brand is Irin, but same pedal is released under different brands such as yuer, joyo, horse(yes, horse brand), even no name. Pcb has a marking on it saying px-40 v1.3. its quite cheap, True bypass, sturdy, noiseless and transparent on flat settings, but what i noticed is that between 0 and 6db on both sidez, response is quite minimal, but between 6 to 12db it changes dramatically.

This instantly reminded me the issue i had with small stone i made before. Using a linear taper had resulted with a massive accumulation of the lfo rate at the end of pots range, so there was so little range to make a fine tuning. This is also quite the same, nearly more than half of the 12db range is ineffective.

I could not entirely remove the pcb to check their tapers, as its a very right fit, i need to bend the enclosure to squeeze it out. maybe i even need to desolder one of them because measuring both ends give me something like 15k of resistance. Mxr s schematics state that they are 50k b taper.

I just wanted to ask, if this case would be the reason of using wrong tapered slider pots, as i would totally expect such cheap stuff from these Chinese people.

[Rob Strand]

I have recently gotten a mxr 10 band eq clone from aliex, its brand is Irin, but same pedal is released under different brands such as yuer, joyo, horse(yes, horse brand), even no name. Pcb has a marking on it saying px-40 v1.3. its quite cheap, True bypass, sturdy, noiseless and transparent on flat settings, but what i noticed is that between 0 and 6db on both sidez, response is quite minimal, but between 6 to 12db it changes dramatically.

It's highly likely the pots are linear when they should be G-taper pots.    What happens with linear pots is all the action occurs in the 0 to 10% and and 90% to 100%.

I just wanted to ask, if this case would be the reason of using wrong tapered slider pots, as i would totally expect such cheap stuff from these Chinese people.

The people making stuff these days are manufacturers.   They copy stuff wrongly make bad decisions to cut costs then you end-up with something that is completely useless.   Not just pedals - everything.   Contrast that against the finely crafted test equipment made in the 60's and 70's which is still operating today.  It's top notch manufacturing and design vs sub-amateur junk.

[ElectricDruid]

It's highly likely the pots are linear when they should be G-taper pots.    What happens with linear pots is all the action occurs in the 0 to 10% and and 90% to 100%.

+1 what Rob said. This is typical for this design of EQ circuit. I came up against the same problem with my Tubescreamer analysis, and posted graphs and details (and a solution, at least for that limited case).

https://electricdruid.net/designing-a-classic-overdrive/

The crucial part is this graph, which shows the EQ response with a linear pot - these lines are every 10% around the pot rotation from 0% to 100%:



The only solutions are to change the pot response to compensate for the EQ response, or to change the EQ response by using a different EQ design so that it gives a sensible result with a linear pot.

[stallik]

i would totally expect such cheap stuff from these Chinese people.

I too expect to buy rubbish from China. That's because they're prepared to make such cheap stuff at a price I'm prepared to pay. Rest assured, they are also capable of making the highest quality, reliable products. So they do. For the worlds most expensive, premium brands

Just saying.

[PRR]

They would need a rarely-made taper. You can't have special order and quite cheap in the same pedal.

Personally I like having a "small tweak" zone and a "big change" zone. But better on a BIG slider, not the bitty 40mm which fits a pedal.

[Baran Ismen]

It has a 20mm travel zone, and i think only tayda has it and its only on 100k g taper with center detent. I ll try to desolder one of them to see What its total resistance.

[Rob Strand]

It has a 20mm travel zone, and i think only tayda has it and its only on 100k g taper with center detent. I ll try to desolder one of them to see What its total resistance.

You might be able to measure in-circuit.   If you set all the pots to the center positions then measure the resistance cross the outside of the pot (pins 1 and 3) you should end up with a resistance which is 1/n times the pot value, where n is the number of bands (per channel).   Now measure the resistance between the wiper and the ends of a few pots - need to analyse the ckt to workout how much the resistance drops with the other pots present.  From those two measurements you should be able to get good idea what the pots are.

[Baran Ismen]

It has a 20mm travel zone, and i think only tayda has it and its only on 100k g taper with center detent. I ll try to desolder one of them to see What its total resistance.

You might be able to measure in-circuit.   If you set all the pots to the center positions then measure the resistance cross the outside of the pot (pins 1 and 3) you should end up with a resistance which is 1/n times the pot value, where n is the number of bands (per channel).   Now measure the resistance between the wiper and the ends of a few pots - need to analyse the ckt to workout how much the resistance drops with the other pots present.  From those two measurements you should be able to get good idea what the pots are.

Volume slider measures between 0 to 18k from top to bottom, whereas 1st band seem to measure 0k - 15k in the middle, and 5k on top. Note that i could only measure the 31hz band, others are inside, cant reach there

Also note that volume slider is the only one that works properly )

[Rob Strand]

Volume slider measures between 0 to 18k from top to bottom, whereas 1st band seem to measure 0k - 15k in the middle, and 5k on top. Note that i could only measure the 31hz band, others are inside, cant reach there

So it looks like 50k pots.

Here's a rough sketch of how it works,

[Baran Ismen]

I finally managed to remove the pcb but my current equipments wont allow me to desolder the upper board im afraid. But i saw 2x tl072 and 2x tl074s inside. No clue about the pots, tho.

[Baran Ismen]

Ok managed to remove one, its b50k.

Need to find some w50k i suppose.

Found these as suitable for type and size, but they are 100k. A parallel between 1 and 3rd lugs of 100k resistor on each of them would work ?

https://www.aliexpress.com/item/32859374842.html?spm=a2g0o.productlist.main.65.52b55204cnwewp&algo_pvid=59dfe93f-ac75-40f4-a17e-3f53fe946e41&algo_exp_id=59dfe93f-ac75-40f4-a17e-3f53fe946e41-32&pdp_npi=4%40dis%21TRY%21211.95%21211.95%21%21%216.77%21%21%40211b446117040500591296226e0c98%2165340498027%21sea%21TR%21179781769%21&curPageLogUid=6iRKTb3ngvN4

[Rob Strand]

Found these as suitable for type and size, but they are 100k. A parallel between 1 and 3rd lugs of 100k resistor on each of them would work ?

It might work and it might work better than the linears.   Parallel resistors won't help at all better off leaving them out.  If you are going down the route of changing pots you would be best hunting down 50k's.

At the end of the day though, you don't know what the design is.  Maybe 50k isn't even a great choice.  If you traced out the circuit you could evaluate exactly what you and what pot value would be most suitable.   If you can see graphic equalizer chips in there then you might be able to make some judgements from that without tracing too much.

If you want to flip the problem completely you could leave the pots and try to redesign the rest of the circuit to work better with 50k linear pots.

[Baran Ismen]

Found these as suitable for type and size, but they are 100k. A parallel between 1 and 3rd lugs of 100k resistor on each of them would work ?

It might work and it might work better than the linears.   Parallel resistors won't help at all better off leaving them out.  If you are going down the route of changing pots you would be best hunting down 50k's.

At the end of the day though, you don't know what the design is.  Maybe 50k isn't even a great choice.  If you traced out the circuit you could evaluate exactly what you and what pot value would be most suitable.   If you can see graphic equalizer chips in there then you might be able to make some judgements from that without tracing too much.

If you want to flip the problem completely you could leave the pots and try to redesign the rest of the circuit to work better with 50k linear pots.

I have to cut 4 connecting bridges to see what's inside, but I saw 2x tl072 and 2x tl074s there. All itty bitty SMDs again.

I have found w50k in a store on Aliex in the same size, think I will order 10 of them. Fingers crossed!

What would happen if I use 100k ? Do i get bigger response than 12db's or half of the range would be inoperative?

[m4268588]

Not a formally defined "G-taper"

[m4268588]

In a real circuits using a real "G taper" pots, no matter how many resistance values of the pot it should be ±12 dB.

[Baran Ismen]

In a real circuits using a real "G taper" pots, no matter how many resistance values of the pot it should be ±12 dB.

Do you mean using 50k or 100k G taper pot would not make a difference? Are you sure?

[FiveseveN]

Are you sure?

Yes. See http://www.geofex.com/article_folders/eqs/paramet.htm

[ElectricDruid]

Are you sure?

Yes. See http://www.geofex.com/article_folders/eqs/paramet.htm

I can't see anything on that page that talks about the amount of cut/boost, the pot taper, or the cut/boost pot value. Where am I supposed to be looking?

[antonis]

Do you mean using 50k or 100k G taper pot would not make a difference? Are you sure?

I think he means it and he's sure..

[FiveseveN]

@ElectricDruid It describes the theory of operation, wherein the pots "pan" between the inverting and non-inverting inputs. So their value doesn't factor in, within reason. Gain is defined by the gyrators' series R and the input and feedback R of the "mixing" stage. This article for example shows the math: https://www.ti.com/lit/an/slyt134/slyt134.pdf